Rheostat



Aug. 16, 1938. K. HOWE 2,127,083

I RHEOSTAT Filed Nov. 13, 1935 2 Sheets-Sheet 1 A ATTORNEY On the inner face of the plate I and surrounding the bearing and engaging the flange Ilia is an insulating disk I2. The outer portion and rear face of this disk is cut away to form a seat for a metal collector ring l3 which has a strip 130, extending outwardly therefrom to a terminal connection 80. mounted in the terminal block 1. A conducting wire or strip i3b connects the terminal 8a to one of the terminals 6, as shown in Fig. 1, for use as a series connected rheostat. The rheostat is readily adapted for use as a potentiometer by omitting the conducting strip I31; and replacing the terminal connection to by a third terminal like the terminals 6.

The contact arm Id of the rheostat is in the form of a flat plate having outwardly bent sides.

Lda and has a large central opening to receive an insulating block l5 which is located between the sides Ila of the contact arm. The block if: has an inwardly projecting circular portion which projects within the central opening of the contact arm and this inwardly projecting portion i5a of the block is cut with concentric spaces as indicated in Fig. 2 for increasing the surface leakage distance. A lug Hb is upset from a central portion of the contact arm and engages a hole in the inner face of the block IS. The insulating block and contact arm are thus held in fixed relationship to each other by the side portions Ila which embrace the sides of the block and the lug Nb which prevents relative longitudinal movement. The contact arm extends outwardly at one end and has a depressed portion Me for engaging the series of contacts 3 successively as the arm is turned. The opposite end of the contact arm has another depressed portion lld as shown in Fig. 2 which engages the collector ring I! on the opposite side of the shaft from the engagement of the other end of the contact arm which engages the contacts 3. The contact arm is rigid throughout all parts and of good conductive material such as hard copper. In rheostats,. where double concentric rows of resistor contacts I are used, the contact arm may have depressed portions He at its opposite ends for engaging the two series of contacts.

The central portion of the insulating block I5 is provided with an enlarged circular cavity in which is seated a spiral spring i6 which encircles the bushing It and serves to impose pressure to force the block l5 and contact arm inwardly so that the contact arm always engages the contacts 3 and the collector ring i3 with sufllcient pressure to maintain a desirable electrical contact at all times and in all positions. The spring is thus insulated in such a way that it cannot carry current and by reason thereof it is not subjected to heating currents which might reduce its tension Moreover, by reason of the contact am making engagement with contacts at its opposite ends and by reason of receiving the spring pressure at its central portion, the pressure imposed upon the contacting portions is always balanced and approximately equalized in any position of the contact arm. In cases where the contact arm has oppositely extending portions of pronounced difference in length, thespring ii, instead of encircling the shaft. may be located to one side thereof and thereby apply the spring pressure to a more central portion of the contact arm. Also, the spring may be of other form than spiral and supported in any suitable manner.

The shaft ll of the rheostat extends through the bushing and is threaded at its opposite ends as shown in Figs.'2 and 4 and is likewise slotted at its opposite ends for providing a locking engagement of the parts without the necessity of usingset screws. For the purpose of holding the spring IS in position and imposing pressure thereon and for locking the movable contact arm and block IE to the shaft, a perforated plate i8 is slid over the inner end of the shaft and seats itself against the spring and between two outwardly extending side portions i5b of the insulating block. The plate l8 has two inwardly v projecting lugs I'oa on opposite sides of its central opening which project into the slot at the end of the shafti'i. Thus the plate i8 is locked to the shaft which plate in turn locks the insulating block and the contact arm to the shaft. Turning of, the shaft will therefore result in turning the contact arm to any position desired. A washer is having lugs I9a which project into the slot in the end of the shaft, is located on the outer face of the plate 18 and the parts are locked in position by the end nut 20 on the inner end of the operating shaft. The use of set screws is thus avoided and also the fixed position of the contact arm and insulating block in relation to the operating shaft is insured and maintained without any chance of the parts working loose.

A sheet metal cover plate 20, which may sometimes be in the form of a skeletonized frame, is mounted on the back of the rheostat and has an inwardly bent rim 20a which is offset at 20b and fits within the rim la of the main rheostat plate and is cut away to fit over and bent to partially cover the terminal block i. A saddle 2 i with inward projections at its ends, embraces the rim of the plate i and the offset portion 20b of the cover plate and is held in place by a screw 22 which has a threaded engagement with the rim of the plate I. Any number of these clips or clamps may be used, three being shown in the drawings spaced apart from each other around the periphery of the rheostat, for holding the cover in place; and supporting feet 23 may also be used as desired for mounting the rheostat in place. These supports 23 may be held in place by the screws 22 on the outside of the saddles 2|, the saddles 2| being provided with outwardly extending bent edges 2la for maintaining the supports 23 in fixed position in relation thereto. The supports for the rheostat may be variously arranged to suit the particular requirements and may readily be mounted in multiple and likewise the shafts in a number of rheostats may be coupled together for multiple control.

The cover plate 20 has a series of separated circular slots 200, as shown in Fig. 3 and on the inside of the cover plate is another circular plate "(I which is rotatably secured to the cover plate 20 by aneyelet 208. The plate 20d is large enough to extend beyond the holes 200 of the cover and affords means for providing an adjustable stop for the contact arm at any desired intermediate position.

A screw 20f passes through any desired one 01' the openings 20c and through the plate 20d and engages a U-shaped angle piece 200, as shown in ill Figs. 2 and 3. By loosing the screw 20! the position of this angle piece may be adjusted as desired through the range of any one slot 20c and by transferring the screw to another slot 200, the range of adjustment may be extended to any portion of the cover plate. The plate 18 is provided with an extension "b at one end and has an outwardly. bent end Hie-which is adapted to engage thestop 20a in its adjusted position. This am'noss auxiliary stop is desirable in cases where a predetermined lirnit of adjustment is fixed for the control of any particular apparatus and the stop 200 is adjusted to such position that the arm no will engage the same at the limiting predetermined position. In order to obtain continuous adjustment of the stop 20g over all portions of the contact arm travel, the piece 200 is provided with two circumferentially spaced tapped holes 20h for receiving the screw 20/. when the limit of adjustment in one of the slots No is reached, the screw "I may be transferred to the other hole ilh which permits adjustment throughout the space occupied by the portions of the cover 20 between the slots "c. The U-shaped piece 209' may also be utilized for locking the contact arm assembly in any fixed position desired. The Li-shaped piece 2001s of such dimensions that its extending portions may embrace the projection Me of the plate II. For locking the parts in any desired fixed position of adjustment. the U- shaped piece is placed to enclose projection lie and the U-shaped piece is then fastened by its screw 20! to remain in any desired position.

The operating handle and the part which 120- operates with the main stop lb for limiting the rotation of the operating shaft at the resistance all out position and the resistance all in position, are mounted on the front end of the operating shaft close to each other. In front of the washer 9 on the shaft I1 is mounted a thrust washer 9b, as shown in Figs. 2 and 4. In front of this washer is mounted a plate 24 having a pointer 24a. 'I 'his pointer also serves the function of cooperating with the main stop lb at the extreme limiting positions of the contact arm. Within the central opening of this plate or pointer projects a pair of oppositely disposed lugs 24b which engage the slot in the front end oi the operating shaft i'l. Thus there is no opportunity for this pointer to work loose or change its position relatively to the shaft i1.

In front of the pointer on the shaft is mounted a metal strip or yoke 25 which extends across the face of the plate 24 and fits over the shaft and is provided with a pair of lugs Zia which extend into the slot at the front end of the operating shaft. It is thus locked to the shaft and maintained in position relatively thereto. The strip 25 is bent forwardly at its ends and again bent inwardly at its ends to form can 251; as shown in Fi 4. A nut 20 is screwed on the front end of the shaft I! to hold the parts in position on the shaft as regards any longitudinal movement thereon. The handle 21 is of a general cylindrical form with scored out central portion. It is provided with a pair of longitudinally extendlng holes at opposite sides through which extend hexagonal rods 20.

,' Zilb and thus form rigid supports for securing the handle in fixed position. The outer ends of these rods have threaded openings which are engaged by screw bolts 29. A circular, face plate or name plate 3| covers the main portion of the outer end of the handle 21 and is located between the head of the screw bolts 2| and the outer ends of the rods 2: and thus serves to hold the. handle in fixed position on the yoke 2i.

c In operation it will be evident am when force is applied to the yoke II for turning the operat- The inner ends of these rods have reduced portions Ila which are' ing shaft when adjusting the rheostat to different positions, theapplication of such force is applied to the shaft at a portion'immediately adjacent to the pointer or "disk 24, and when the latter.

I It is also evident that the structure is sturdy and dependable in long continued use without likelihood of the parts working loose or being displaced from their proper relative positions. Also, by reason of the rigid structure of the contact arm throughout and its balanced application of contact pressure, the maintenance of good electrical contact at all times and in all positions of the rheostat is assured.

Although a preferred form of the invention has been described, the same may be applied in various features thereof to other forms of rheostats than the particular type shown, and-to a wide range of rheostats of different capacities; also various modifications may be made therein without departing from the scope of the invention. a

The invention claimed is:

1. A rheostat comprising a rotatable shaft, a contact arm operated by said shaft, 8. stop mounted on the face of the rheostat, a pointer having a portion extending within an opening of said shaft and adapted to engage said stop, a plate having a portion extending within an opening of said shaft andhaving oppositely bent portions, operating means for rotating said shaft mounted on said oppositely bent portions and spaced thereby from the end of said shaft, and means for holding said pointer and said plate in position on said shaft.

2. A rheostat comprising a plate, a rotatable shaft, a contact arm operated by said shaft, a

of the rheostat and also having a portion bent over and in front of said encircling portion of the stop disc for holding said sleeve in fixed position on said plate and for likewise holding said stop disc in fixed position with reference to said, plate.

3. A rheostat comprising a plate carryinghxed contacts, a sleeve fixed to said plate, a shaft journalied in said sleeve, an insulating block rotatably and slidably mounted'on said sleeve, a rigid contact arm coupled with said block and rotatably driven by said block, a plate fixed to said shaft to turn therewith, said last named plate having a locking driving connection with said block for rotating the same while permitting 4. A rheostat comm H i I contacts, a sleeve fixed to said plate, a'shaft journallcd in said sleeve, an insulating block rotatably and 'slidably mounted on said sleeve, a rigid con 75 tact arm coupled with said block and rotatably driven by said block, a plate fixed to said shaft to turn therewith, said last named plate having a locking driving connection with said block for rotating the same while permitting relative axial movement thereof, said block having a central recess formed in the rear face thereof, and a spring between said last named plate and said block and seated in said recess to cause said block to impose pressure onsaid arm to hold said arm in contact with said fixed contacts. I

5. A rheostat comprising a plate carrying fixed contacts, a sleeve fixed to said plate, a shaft Journalled in said sleeve, an insulating block rotatably and slidably mounted on said sleeve, a rigid contact arm coupled with said block and rotatably driven by said block and having a central aperture of a size to prevent contact with said sleeve, said block having a channel formed across the rear face thereof, a plate fixed to said shaft to turn therewith and fitting in said channel to cause rotation of said block and arm, said channel being sufiicientlv deep to permit axial movement of said block with respect to said last named plate, and a spring seated between said last named plate and said block to cause said block to impose pressure on said arm to maintain said arm in contact with said fixed contacts.

6. A rheostat comprising a plate carrying fixed contacts, a sleeve fixed to said plate, a shaft Journalled in said sleeve, an insulating block rotatably and slidably mounted on said sleeve, a rigid contact arm coupled with said block and rotatably driven by said block and having a central aperture of a size to prevent contact with said sleeve, said block having a channel formed across the rear face thereof, a plate fixed to said shaft to turn therewith and fitting in said channel to cause rotation of said block and arm, said channel being sufliciently deep to permit axial movement of said block with respect to said last named plate, said block having a central recess on the rear face thereof, and a spring between said block and said last named plate and seated in said recess to cause said block to impose pressure on said arm to hold the said arm in contact with said fixed contacts.

'I. A rheostat comprising a plate carrying fixed contacts. a sleeve fixed to said plate, a shaft Journalled in said sleeve, an insulating block rotatably and slidably mounted on said sleeve, a rigid contact arm coupled with said block and rotatably driven by said block, said contact arm extending to engage contacts on opposite sides of said shaft, a plate fixed to said shaft to turn therewith, said last named plate having a locking driving connection with said block permitting relative axialmovement thereof, and a spring seated between said block and said last named plate to cause said block to impose pressure on said arm to maintain said arm in con-- tact with said fixed contact.

3. A rheostat comprising a plate carrying fixed contacts, a sleeve fixed to said plate, a shalt journalied in said sleeve, an insulating block rotatabiy and slidably mounted on said sleeve, a rigid contact arm coupled with said block and rotatably driven by said block, a plate fixed to said shaft to turn therewith, said last named plate having a locking driving connection with said block for rotating the same while permitting relative axial movement thereof, a spring seated between said block and said last named plate to cause said block to impose pressure on said arm to maintain said arm in contact with said fixed contacts, and a cover for the rheostat. said cover having a projecting stop and said last named plate being adapted to engage said stop to limit the movement of said arm.

9. A rheostat comprising a plate carrying fixed contacts, a sleeve fixed to said plate, a shaft journalled in said sleeve, an insulating block rotatably and slidably mounted on saidsleeve. a rigid contact arm coupled with said block and rotatably driven by said block, a plate fixed to said shaft to turn therewith, said last named plate having a locking driving connection with said block for rotating the same while permitting relative axial movement thereof, a spring seated between said block and said last named plate to cause said block to impose pressure on said arm to maintain said arm in contact with said fixed contacts, a cover for the rheostat, and an inwardly projecting stop mounted on the inner face of said cover and adjustable circumferentially, said last named plate being adapted to engage said stop to limit the movement of said arm.

10. A rheostat comprising a plate carrying fixed, contacts, a sleeve fixed to said plate, a shaft Journalled in said sleeve, an insulating block rotatably and slidably mounted on said sleeve, a rigid contact arm coupled with said block and rotatably driven by said block, a plate fixed to said shaft to turn therewith, said last named plate having a locking driving connection with said block for rotating the same while permitting relative axial movement thereof, a spring seated between said block and said last named plate to cause said block to impose pressure on said arm to maintain said arm in contact with said fixed contacts, a cover for the rheostat, a member having an inwardly projecting stop mounted on the inner face of said cover, and means for adjusting said member circumferentially comprising setting means carried by said member and extending through an arcuate slot in said cover, said last named plate being adapted to engage said stop to limit the movement of said arm.

KASSON HOWE. 

